1. Field of the Invention
This invention relates to titanium-based nanocrystalline alloys, which are formed by conventional solidification of alloy melts, or by cooling the high temperature solid phase to room temperature to obtain a metastable body-centered cubic .beta. crystalline phase, followed by annealing at a relatively lower temperature for an extended time to let this metastable phase transform to other more stable phases, whereas the process of nucleation and growth of nuclei are controlled by the selected annealing temperature and time so as to obtain nanocrystalline and amorphous materials.
2. Description
Increased interest on the synthesis of nanocrystalline materials in recent years dates back to the pioneering investigations of H. Gleiter in 1981. He synthesized ultra-fine metallic particles using an inert gas condensation method and consolidated them in situ into small discs under ultra-high vacuum conditions. Since then a number of techniques have been developed in which the starting material is in gaseous state (Inert gas condensation, Sputtering, Plasma processing, Vapor deposition), liquid state (Electrodeposition, Rapid solidification, Pressure-quenching), or solid state (Mechanical alloying, Sliding wear, Spark erosion, Crystallization of amorphous phase).
Most of the early results were based on materials produced by gas condensation technique, and porosity was an internal part of the materials. The properties and structures of these materials were interpreted on the basis of a two component mixture--crystalline and interfacial components--whereas they should have been interpreted by taking the porosity into account as well. In fact, reduction in Young's modulus values, increased diffusivities, and in general, variations in mechanical and physical properties have now been ascribed to the presence of porosity in these materials.
Wide-spread use and search for technological application of nanocrystalline materials require the availability of large quantities of well characterized materials with reproducible properties; and this needs to be done economically. Therefore, development of large-size bulk nanocrystalline materials without porosity is an urgent necessity.
Titanium-based alloys have been extensively used in a variety of applications, such as structural materials for aircraft, automobiles, or as body parts mainly because of their high strength-weight ratio. Now attempts are still being made to enhance tensile strength while decreasing the density.